1. Field of the Invention
The present invention relates to a room-temperature ionic liquid and a power storage device using the room-temperature ionic liquid.
Note that the power storage device indicates all elements and devices which have a function of storing power.
2. Description of the Related Art
A lithium-ion secondary battery which is one of power storage devices is used in a variety of applications including mobile phones, electric vehicles (EV), and the like. Characteristics such as high energy density, cycle characteristics, and safety under various operating environments are required for a lithium-ion secondary battery.
As an organic solvent for an electrolyte of a lithium-ion secondary battery, a cyclic carbonate which has high dielectric constant and excellent ion conductivity is often used. Among the cyclic carbonate, ethylene carbonate is often used.
However, not only ethylene carbonate but many organic solvents have volatility and a low flash point. For this reason, in the case where an organic solvent is used for an electrolyte of a lithium-ion secondary battery, the temperature inside the lithium-ion secondary battery might rise due to a short circuit, overcharge, or the like and the lithium-ion secondary battery might burst or catch fire.
In view of the above, it has been considered to use a room-temperature ionic liquid which is less likely to burn and volatilize as an electrolyte of a lithium-ion secondary battery.